In an image-based overlay measurement apparatus, with the decrease in the size of a measurement subject device, the requirement for the accuracy in overlay has intensified. Therefore, the number of sampling points has been increasing to perform accurate overlay measurement. In a case of disposing a mark for overlay measurement on a reticle used in a lithographic process, the mark is disposed on a scribe line in a shot area. With the heightened demand for the accuracy in overlay measurement, marks for overlay measurement that need to be disposed in the shot area are increasing in number. In order to increase the number of marks disposable on the scribe line, it is necessary to reduce the size of each mark for overlay measurement.
The image-based overlay measurement apparatus uses an optical microscope to perform overlay measurement. Therefore, if the size of the mark for overlay measurement is reduced, the lens aberration of an optical microscope is likely to influence the accuracy of overlay measurement. Specifically, in a case where the optical microscope (optical measurement system) has comatic aberration which is odd function aberration, there is a possibility that an optical image of the mark for overlay measurement will shift, thereby increasing an error of the overlay measurement.